In the gas turbine engine art, particularly those developed for use in aircraft, high temperature operating components are exposed to strenuous oxidizing conditions during operation. Typical of such components are the blades, vanes and associated parts disposed in the turbine section of such engines. In order to extend the operating life of such articles, designers have specified coatings for application to article surfaces for oxidation as well as sulfidation protection.
One such coating has been reported as a thermal barrier coating system in a variety of forms. Generally, the thermal barrier coating is a ceramic type coating, examples of which include zirconia generally stabilized with yttria, magnesia or calcia. A preferred form of such a system includes a bond coating disposed between the substrate and the ceramic thermal barrier coating. Reported have been bond coatings of the M Cr Al type of alloy in which M is a metal selected from Fe, Ni, Co and their mixtures and alloys. Other elements including Y, rare earths, Pt, Rh, Pd, Hf, etc., and their combinations have been included in such an M Cr Al alloy to enhance selected properties. Typical U.S. Patents describing such a system or elements thereof include 4,055,705 - Stecura, et al. (patented Oct. 25, 1977); 4,269,903 - Clingman, et al. (patented May 26, 1981); 4,321,310 - Ulion, et al. (patented Mar. 23, 1982); 4,321,311 - Strangman (patented Mar. 23, 1981); 4,335,190 - Bill, et al. (patented Jun. 15, 1982) and 4,880,614 - Strangman (patented Nov. 14, 1989). The disclosure of each of these references is hereby incorporated herein by reference. For example, there is described in the disclosure of 4,880,614 - Strangman a chemical vapor deposited (CVD) interfacial layer of a high purity, dense ceramic oxide of alpha alumina deposited over an M Cr Al Y bond coat, and between the metal bond coat and the ceramic thermal barrier coating. Optionally, a diffusion aluminide can be included at the surface of the substrate, beneath the bond coat.
Methods for applying known systems, such as are described in the above incorporated patents, require vacuum or low pressure application systems which are difficult to control, require expensive, complex equipment and can have a lower production efficiency. Accordingly, the resultant coatings systems and articles are expensive to manufacture.